1. Field of the Invention
The present invention relates to a method of displaying a digital photograph, particularly on a monitor.
2. Description of the Related Art
A digital photograph can be produced by scanning a photograph and converting it into a matrix of image data. The image data can then be bitmapped into a matrix of pixels which together form a grey-scale image reproduction of the original photograph. The grey-scale image can be displayed on an electronic display device, such as a computer monitor.
A problem when running in either WINDOWS or OS2 is that the grey-scale bitmapping algorithm used with these programs incorporates only a single color table having 256 color value entries. The color table matches each of the 256 monochrome shades of grey that are included in the pixel data with 8-bit color component intensity values for each of red, green and blue. When the intensity values are set equal for each of these three colors, a monochrome shade of grey is produced by the monitor. Use of the color table reduces the amount of data to be stored for each pixel from 24 bits (eight bits for each of red, green and blue) to 8 bits (enough to identify one of the 256 entries in the color table).
The single color table used with WINDOWS or OS2 is just sufficient to accommodate the 256 shades of grey normally used to produce a monochrome display. Thus, there is no allowance in the bitmapping algorithm for including non-monochrome or colored elements within the display of the monochrome image of the digital photograph.
In order to electronically display only a selected object or component from within the photograph, a component bitmap can be cut from the digital photograph based bitmap, converted to monochrome, and edited in other ways by using a bitmap editor and a set of task-specific software tools. The selected component of the photograph can then be displayed against a background chosen by the user, as illustrated by example in FIG. 1. A problem is that the cut edges 10 of the selected component 12 appear to be very jagged, particularly when the cut edges 10 are adjacent to a monochrome background 14. The reduction in quality caused by the jagged edges 10 varies, depending upon the angles of the lines forming the edges of the picture, and the color difference between the picture edge 10 and the background 14.
It is known, in some circumstances, to use a bitmap editor to manually improve the quality of the original component bitmap edges. This approach is not practical, however, for three reasons. First, it is very labor intensive and must be repeated for each component. Second, the edges that are adjacent to the background vary. For example, if a second component that is adjacent to or behind the first component in the photograph is also included in the displayed image, a portion of the edge of the first component will be adjacent to the second component, rather than to the background. Third, different monochrome background colors are used by different host utilities. Thus, for adequate blending of the picture into the monochrome background color, different quality improvements must be made depending upon which monochrome background color is being used. It is possible to scale or reduce the size of the component picture depending on the amount of screen area that is to be dedicated to displaying the picture. In other words, the number of pixels available with which to display the image on the screen may be less than the number of pixels in the original digitized image. Known methods of scaling color bitmaps when the monitor is in "256 color" mode are too slow, or require bitmaps that are too large and/or lacking in quality.
One such known method of scaling is to throw away rows and/or columns of information. This method is very fast, but generally results in very poor quality. Another known method is to use some algorithm such that each pixel in the original image contributes to the value of one or more pixels in the scaled down image. When using this method with a color bitmap, a large "24 bit per pixel" bitmap is required for good quality. When the PC display is in "256 color" mode, the new pixel values that are computed must be mapped to the closest matching color in the system's "256 color" palette. That required color mapping is a very slow process, and the color approximations often result in poor quality.
What is needed in the art is a practical method of assembling, scaling, enhancing and displaying digital photograph quality bitmaps in an environment where the image must change quickly.